Preheat the oven to 220C/425F/Gas 7.
Place one pastry disk on a baking sheet and top with the leeks and blue cheese, leaving a 1cm/½in border all around.
Brush the clean pastry border with the beaten egg and top with the second pastry disk. Press down the edge to seal the pastry disks, and brush all over the top with the remaining egg.
Place into the oven to bake fo r8-10 minutes, or until golden and risen.
To serve, place onto a warmed plate and garnish with the parsley.